Page 36 - Climate Control News Magazine
P. 36

Combining CO2 and ammonia for
industrial applications
THE LARGE INDUSTRIAL REFRIGERATION MARKET IS NO STRANGER TO THE USE OF NATURAL REFRIGERANTS. EMERSON'S DIRECTOR OF FOOD RETAIL MARKETING AND GROWTH STRATEGY FOR THE COLD CHAIN, ANDRE PATENAUDE, EXPLAINS WHY AMMONIA (AKA NH3 OR R-717) HAS BEEN THE BACKBONE OF MANY COLD STORAGE APPLICATIONS FOR MANY DECADES.
SELF-CONTAINED SYSTEMS
Meeting high-tonnage, cold storage require- ments while addressing the known operational challenges of ammonia and CO2 meant that manufacturers have had to expand upon the ex- isting cascade architecture. Among the leading solutions to achieve this is a self-contained sys- tem that integrates an entire NH3/CO2 cascade system into a modular refrigeration unit.
Designed to be located on the rooftop or next to a building of a cold storage facility, this modu- lar refrigeration unit combines CO2 and NH3 compression technologies and electronic con- trols in a cascade system that contains two inde- pendent CO2 and NH3 circuits with separate condensers and evaporators (including a shared cascade heat exchanger).
The NH3 portion of the cascade system pro- vides the high stage of the refrigeration cycle, uti- lizing a small-displacement, very low-charge, single-screw compressor and a condenser that sits on top of the unit and uses ambient air to cool it; liquid ammonia evaporates in the cas- cade heat exchanger. This design meets the low-
André Patenaude is director of food retail marketing and growth strategy, cold chain, at Emerson.
MORE RECENTLY, THE in- creasing uptake of CO2 (R-744) in commercial applications has led refrigeration manufacturers to look for ways to exploit this emerging natural refrigerant in industrial appli- cations — and the technology to combine the ben- efits of both refrigerants and facilitate this transi- tion - which is finally coming of age.
With excellent performance efficiency and ul- tra-low environmental impact, in many ways NH3 is the closest thing to the perfect refriger- ant. However, it has one major caveat: toxicity.
In recent years, tightening regulations by the Oc- cupational Safety and Health Administration (OSHA) have sought to improve the safety of NH3 systems. Operators are now required to provide doc- umentation for systems charged with at least 10,000 lbs of ammonia, per OSHA’s Process Safety Manage- ment of Highly Hazardous Chemicals standard.
For these reasons, operators and manufactur- ers alike began looking for ways to leverage am-
monia’s efficiency while lowering system charges necessary to limit the potential for exposure to workers and product spoilage. Enter NH3/CO2 cascade technology, a system architecture that has been successfully deployed in many commer- cial applications with HFCs on the high side.
To make the transition to the large industrial market, manufacturers first needed to find a way to deliver high-tonnage refrigeration capacity while keeping ammonia charges low to help miti- gate safety concerns, ease documentation re- quirements and, if possible, avoid the potential for exposure in any occupied spaces. They also need- ed to address other prevailing concerns about the use of NH3/CO2 cascade systems, including:
Complexities related to installation, commis- sioning, operation and servicing requirements. Potential heat exchanger leaks of CO2 and NH3 that can mix and create ammonium carbamate, resulting in system failure.
Maintaining uptime during the transition from a legacy system to a new cascade system.
CLIMATECONTROLNEWS.COM.AU
36


































































































   34   35   36   37   38